Temperature control system



July 14, 1942. J. w. MYERS 2,289,882

- TEMPERATURE CONTROL SYSTEM Filed June 12, 1941 L fohn Wl lye/r's,

Patented July 14, 1942 2,289,882 rnmnnaruan coN'raor. SYSTEM John W. Myers, Quincy, 111. Application June 12,.1941, Serial No. 397,826

4 Claims.

This invention relates to improvements in temperature control systems and particularly to a system for controlling thetemperature in the interior of incubators.

The primary object of the invention is to provide a temperature control system for incubators, wherein mechanism is provided for rendering the heating unit inoperative when the temperature within the incubator rises to a predetermined degree-and, in the event such mechanism fails to a signal or alarm will be given as a warning of the failure of the control mechanism to render the heating means inoperative.

Specifically, the present control system comfunction to render said heating unit inoperative,

prises an electrical heating element connected in an electrical circuit containing a, so-called, operating switch, in the form of a one-way switch, and a, so-ca1led,.safety switch, in the form of a double-throw switch. this latter switch normally being closed to close the heating element circuit, but, when thrown to open that circuit, it will close the alarm circuit. Temperature-responsive mechanism is provided for opening the normally closed operating switch and, upon failure ofthat switch to be opened when a predetermined temperature is reached, the said mechanism will actuate the double-throw safety switch, thus opening the heating element circuit and closing the alarm circuit.

Still another object of the invention is to provide means for rendering the alarm circuit inoperative irrespective of the double-throw safety switch, so that, in the event it is desired to continue operation of the incubator over a period of time when the, so-called, operating switch cannot be manipulated to open the heating element circuit, said alarm will .not be intermittently sounded each time the double-throw safety switch is actuated by the heat-responsive mechanism to open the heating element circuit.

With these and other objects in view, themvention consists in certain details of construction and combinations and arrangements of parts, all as will hereinafter be more fully described and the novel features thereof particularly pointed out in the appended claims.

In the accompanying drawing- Figure l is a perspective view, partly broken away, illustratingprimarily the temperature-responsive devices for actuating the switches in volved in the electrical heating element circuit; and

Fig. 2 is a diagrammatic illustration of the circuits for the heating element and alarm.

The heating element It which is suitably located in the interior of the incubator structure has one terminal connected to one side I I of the main feed line. The other terminal of said heating element is connected by line it to one contact 22 of a double throw switch it, known as the safety switch, and the movable contact member I! of said safety switch is connected by line It to the fixed contact member I I of the singlethrow operating switch l8 whosemovable contact member I! is connected by line 20 to the power switch 2| which, in turn, is connected to the other side ll of the main feed line. The second fixed contact ll of the double-throw safety switch It is connected by line 23 to transformer 24 which. in turn, is connected by line 25 to an alarm, preferably audible, such as a bell or buzzer 28. A return line 25" also connects thebell or buzzer, and transformer, and a line 21 connects the transformer to the main feed line I l Normally, the operating switch It is closed and the movable contact I! of the double-throw safety switch is normally in engagement with the fixed contact 22, so that, when the power switch 2| is closed, the heating element III will be energized and the alarm circuit will be opened.

In order to regulate the temperature in the interior of the incubator, temperature-responsive means are provided for actuating the operating switch It and,the safety switch I to open the heating element circuit when the temperature in the incubator rises to a predetermined degree.

For instance, a, so-called, double-wafer thermostat 28, carried on an adjusting screw 29, is adapted to engage an actuating member in the form of a lever 30 when the thermostat expands under the influence of the heating when the temperature rises to the predetermined degree. One end of said lever 30 is adapted to engage an actuating plunger 3| of the operating switch l8 when said lever is ultimately depressed by the thermostatic control devices. Plunger 3|, when depressed by lever 30, is adapted to open the operating switch it, thus breaking the heating element circuit. Snap switches are usually used in devices of the present type and, due to arcing, their contact points frequently become welded together, so that the switch has an inclination to stick, in which case, when used in an incubator or brooder, the temperature can run up so .high before it is noticed that the eggs are spoiled, or, in the case of brooders, the chicks are killed. To provide against the operating switch l8 sticking, the actuating plunger 3| of that switch is of the spring type, being composed of telescoping sections yieldingly held in certain positions axially of one another by a spring 3i, so that, when lever 30 is first depressed, the plunger as a whole will move and, upon failure of the operating switch to open, the inner section of the plunger can be further depressed against the pressure of spring 3h. Due to this additional movement permitted the lever 30, the opposite end of said lever can be utilized to actuate the double-throw safety switch M to break the heating element circuit by disengaging movable contact iii from fixed contact 22 of said safety switch. As illustrated, the lever 3i carries a set screw 82 adapted to engage the actuating plunger 88 or the double-throw safety switch. Thus, if depression of the actuating plunger 38 of the operating switch fails to open that switch, continuous depression of lever so aeeasaa will cause actuating plunger 33 of the safety switch to be operated to break the heating element circuit. In actuating the movable contact 85 of the safety switch out of engagement with the fixed contact 32, said movable contact ongages contact is of the alarm circuit, thus closing this latter circuit and sounding the alarm, so that the operator will mow that the apparatus is not functioning entirely properly and that the heating element has been cut on.

It will be appreciated that the additional throw of lever 30 that is required to operate actuating plunger 33 of the safety switch determines the additional rise in temperature that is permitted before the heating element is de-energized. In order that this additional rise, over and above what would be the normal highest temperature desired, can be minimized, and, in order to increase the accuracy with which the temperatures are controlled, the set screw 32 is adjustable in the lever 30, so as to vary the distance by which it is normally spaced from the actuating plunger 33 -of the safety switch, and, by adjusting the screw 29 carrying the thermostatic control devices 28,the extent to which said thermostatic devices must expand before lever 30 is depressed can readily be regulated.

It will be understood that both the operating switch l8 and the safety switch l4 automatically return to their positions for closing the heating element when the pressure exerted on their respective actuating plungers by lever 30 is relieved. Hence, upon sounding of the alarm, if the operator should fail to take proper steps to immediately remedy defects that may have occurred in the control system, the temperature within the incubator will gradually fall until the thermostatic control devices 28 have contacted to a point where the pressure on actuating plunger 33 of the safety switch will be relieved, under which circumstances that switch will again close the heating element circuit to de-energize the heating element. This movement of the doublethrow safety switch will result in the breaking of the alarm circuit, but, when the temperature within the incubator has again risen to the proper degree, the safety switch actuating the plunger will again be actuated to open the heating element circuit and closethe alarm circuit. If it should be desired to permit the incubator to continue to operate in-this fashion until'the necessary repairs can be made, it might be desirable to render the alarm inoperative temporarily, so

that it will not be intermittently energized each time the temperature rises to a point where the double-throw safety switch is actuated. For this reason, it is preferred that a manually operable switch 34 is interposed in line 23. which constitutes a part of the alarm circuit. In this fashion, by opening switch 34, the alarm circuit, can be temporarily'maintained open until the operator sees flt to restore switch 34 to closed position.

The relative positions of the several inst'ru-- 'mentalities, such as the spacing of the expansible thermostatic member with respect to the operating lever 30 and the spacing of said lever with respect to the actuating plungers ofv the operating switch and safety switch, can be regulated with an extreme nicety so that a rise 01' less than I one degree in temperature will be all that is necessary to cause the lever 3E5 to depress the actuating plunger oi the safety switch after depression of the actuating plunger of the operating switch, assuming that this latter switch fails to open. Preferably, a spring 35 is coiled around the set screw 32 to hold said screw in the desired position of adjustment.

With the present system, it will readily be appreciated that temperatures within the incubator or brooder can not only be very accurately controlled, but the danger of losing the eggs or chicks by overheating is practically eliminated.

' What I claim is! 1. In a temperature control system for incubators, a heating circuit, a normally closed operating switch in said heating circuit, a. plungerIfor opening said switch, a. normally closed safety switch in said heating circuit, a plunger for opennormally open alarm circuit including said safety switch, movement of said safety switch by the plunger to open the heating circuit also serving to close said alarm circuit.

2. In a temperature control system for inc'ubators, a heating'circuit, a normally closed operating switch in said heating circuit comprising an actuating member for opening said switch, a normally closed safety switch in said heating circuit comprising an actuating member for opening said heating circuit, a lever movable into engagement with said actuating members to open the operating and safety switches in sequence, means for varying the extent of movement required of said lever for opening one of said switches, heat-responsive means for moving said lever, and an alarm circuit controlled by said safety switch, said alarm circuit being closed when said safety switch is actuated toopen the heating circuit.

3. In a temperature control system for incubators, a heating circuit comprising two switches each having two contacts normally closed to maintain said circuit closed, one of said switches comprising a third contact, a normally open signal circuit in which said third contact is included, and temperature-responsive means operatively associated with one contact .of each of said switches to actuate said switches to successively open the contacts which normally ,maintain'the heating circuit closed and to establish the signal circuit through said third contact.

4. In a temperature control system for incubators, a heating circuit comprising two switches each having two contacts normally engaging one another to close said circuit, plungers engaging one contact of each switch, a third contact in one of said switches, a signal circuit in which said third contact is included, a lever engaging said plungers, and temperature-responsive.means for rocking said lever, movement of said lever a predetermined distance being adapted to depress the plunger for the two-contact switch and open said heating circuit, and movement of said lever in the same direction in excess of said prede- 'termined distance being adapted to depress the normally closed 7 JOHN W. MY ERS. 

